742 THE VOYAGE OF H.M.S. CHALLENGER. 



slender, cylindrical, and a little longer than the carapace, the former is broad at the base, 

 and then suddenly tapers to a slender termination which is subequal with the inner in 

 length; the lower surface is thickly matted with closely packed membranous cilia that 

 stand on the rounded surface, and not in a hollow as in some genera. 



The second pair of antennae (fig. lc) carries a long and pointed scaphocerite that is 

 but little shorter than the rostrum ; the inner or foliaceous portion tapers to the 

 apex, where it gradually merges into the strong distal tooth ; the outer margin is 

 strengthened by a ridge which falls between two rigid and strong teeth standing on the 

 outer and distal margin of the second joint of the peduncle. On the outer side of the 

 ridge the upper tooth checks the backward action of the outwardly extended scaphocerite 

 by falling into a longitudinal groove (fig. lc"), and pressing against the elevated ridge on 

 that side, and so making this organ an efficient weapon of offence. 



The mandibles (fig. Id) are deeply embedded in the oral cavity between the cheilo- 

 glossa in front (ch.a), which extends into and fills the cavity between the mandibles (d) 

 and the metastomata (m.a.), which falls against them posteriorly. The psalistoma is broad, 

 thin, concavo-convex, and serrate at the margin ; it is continuous with the molar process, 

 and carries a two-jointed synaphipod, of which the first joint is long, and the second 

 short and disc-shaped. 



The first pair of siagnopoda (fig. le) does not differ much from that of other allied 

 genera ; it is small, of considerable tenuity, and three-branched, the two inner branches 

 being tipped with short, stiff spinules, and the outer smooth, membranous, and obtusely 

 pointed. 



The second pair (fig. If) consists of three broad plates of extreme tenuity, and one 

 short and narrow ; one of the inner plates is divided into two, and fringed on the inner 

 margin with numerous closely packed short spinules, the inner basal one with long and 

 slender hairs ; the central is short, narrow, and obtusely pointed, and the outer is 

 developed into a large mastigobranchial plate of extreme tenuity, and fringed with cilia, 

 all directed anteriorly in a centrifugal manner. 



The third pair of siagnopoda (fig. Ig) has three plates ; the outer plate is broad, 

 curved, and of great tenuity, and fringed with hairs ; the concave inner margin is reflexed 

 at nearly right angles longitudinally ; at the base is a bifid mastigobranchial plate, free 

 from hairs or cilia. 



The first pair of gnathopoda is subpediform and seven-jointed ; the terminal joints 

 are reflexed, the basis carrying a long ecphysis, and the coxa a small mastigobranchial 

 plate and podobranchial plume. 



The second pair (fig. li) is pediform and five-jointed ; the coxa carries a lunate disc-like 

 plate, of which the upper horn is bifid, while to the lower horn is attached a short and 

 rudimentary membranous mastigobranchial plate, and near the centre of the crescent a 

 small podobranchial plume. The basis carries a slender ecphysis that is two-thirds of 



